It's poised to be a low-key affair — much like the sluggish early days of the Republican contest itself.

The Republican who is so far leading the 2012 nomination field, Mitt Romney, won't be attending the debate. Neither will any other big-name Republicans weighing bids, like Sarah Palin, or celebrity hopefuls, like Donald Trump.

"Without any of the front-runners, you really can't call it a debate," said Rick Beltram, a former Republican chairman in Spartanburg County.

Still, Republicans hope to get some publicity from the event in the city of Greenville, because South Carolina is an early primary state important for Republican hopes of retaking the White House from Democratic President Barack Obama.

They're the only candidates who met the sponsors' criteria to participate. Fox News and the South Carolina Republican Party required all participants to have formed a presidential exploratory committee, filed state Republican Party paperwork and paid $25,000 to get on the primary ballot.

Criticism of Obama, the Democrat they hope to have the chance to challenge next year, is likely. And the candidates may even seek to try to differentiate themselves from Romney, the former Massachusetts governor who many consider the closest to a front-runner in a field that lacks one.

Romney has created an exploratory committee but he opted out of participating. He's been choosing his audiences carefully, and his advisers see little benefit in Romney attending.

"It's still early, the field is too unsettled, and he's not yet an announced candidate," Matt Rhoades, a top Romney adviser, said in a statement.

He may face fierce opposition from secular groups and progressives who argue that his religious rhetoric violates the separation of church and state and that his belief that some groups, such as the Boy Scouts of America, should be allowed to discriminate against gays is bigoted.

Huntsman, who is Mormon, worked as a missionary in Taiwan and is fluent in Mandarin. But his moderate credentials — backing civil unions for gays and the cap-and-trade energy legislation — could hurt him in a GOP primary. So could serving under Obama.

Michele Bachmann, announced on June 13

Larry Downing
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REUTERS

Rep. Michele Bachmann

Born and raised in Iowa, this Tea Party favorite and Minnesota congresswoman announced during a June 13 GOP debate that she's officially in the running for the Republican nomination.

Bachmann tells The Associated Press she decided to jump into the 2012 race at this time because she believed it was "the right thing to do."

She's been criticized for making some high-profile gaffes — among them, claiming taxpayers would be stuck with a $200 million per day tab for President Barack Obama's trip to India and identifying New Hampshire as the site of the Revolutionary War's opening shots.

But Bachmann's proved a viable fundraiser, collecting more than $2 million in political contributions in the first 90 days of 2011 — slightly exceeding the $1.8 million Mitt Romney brought in via his PAC in the first quarter.

Rick Santorum, announced on June 6

Charlie Neibergall
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AP file

Former Penn. Sen. Rick Santorum

A staunch cultural conservative vehemently against abortion and gay marriage, the former Pennsylvania senator hopes to energize Republicans with a keen focus on social issues.

No stranger to controversy, Santorum was condemned by a wide range of groups in 2003 for equating homosexuality with incest, pedophilia and bestiality. More recently, Santorum faced criticism when he called Obama’s support for abortion rights “almost remarkable for a black man.”

The former Massachusetts governor and 2008 presidential candidate has spent the last three years laying the foundations for another run at the White House — building a vigorous political action committee, making regular media appearances, and penning a policy-heavy book.

In April, he announced, via YouTube and Twitter, that he'd formed an exploratory commitee. Romney made his run official in Stratham, N.H., on June 2.

The former CEO of consulting firm Bain & Company and the president of the organizing committee for the 2002 Winter Olympics in Salt Lake City, Romney frequently highlights his business background as one of his main qualifications to serve as president.

To capture the nomination, Romney will have to defend the health care overhaul he enacted during his governorship — legislation that bears similarities to the Obama-backed bill despised by many conservatives. He'll also have to overcome the perception of being a flip-flopper (like supporting abortion rights in his 1994 and 2002 bids for office, but opposing them in his '08 run).

In the first quarter of 2011, he netted some $1.8 million through his PAC "Free and Strong America."

Herman Cain, announced on May 21

Brendan Smialowski
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Getty Images file

Talk show host Herman Cain

Cain, an Atlanta radio host and former CEO of Godfather’s Pizza, has support from some Tea Party factions.

An African-American who describes himself as a “citizen’s candidate,” he was the first Republican to form a formal presidential exploratory committee. He officially entered the race in May, telling supporters, "When we wake up and they declare the presidential results, and Herman Cain is in the White House, we'll all be able to say, free at last! Free at last! Thank God almighty, this nation is free at last, again!"

Prior to the release of President Obama's long-form birth certificate, Cain rehashed the birther theory, telling a Florida blogger, “I respect people that believe he should prove his citizenship ... He should prove he was born in the United States of America.”

Ron Paul, announced on May 13

Cliff Owen
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AP file

Rep. Ron Paul

In 2008, Texas congressman Ron Paul’s libertarian rallying cry — and his opposition to the Iraq and Afghanistan wars — did not fall on deaf ears. An idiosyncratic foe of the Federal Reserve and a passionate advocate for limited government, Paul mounted a presidential run that was characterized by bursts of jaw-dropping online fundraising.

The former speaker of the House who led the 1994 “Republican Revolution,” Gingrich remains a robust presence on the GOP stage as a prolific writer and political thinker. In recent years, Barack Obama has provided a new target for the blistering critiques Gingrich famously leveled at President Bill Clinton.

In early May, he made his 2012 run official. "I have been humbled by all the encouragement you have given me to run," Gingrich wrote on Facebook and Twitter.

But a month later, the campaign was practically in ruins — with his campaign manager, spokesman, senior strategists all resigning en masse. Most cited issues with the "direction" of the campaign. But Gingrich vowed to press on.

Also at issue: Gingrich’s personal life could make winning the support of social conservatives thorny for the twice-divorced former lawmaker. In a damning interview earlier this year, Esquire quoted one of Gingrich’s former wives describing him as a hypocrite who preached the sanctity of marriage while in the midst of conducting an illicit affair.

Additional obstacles include his recent criticism of Rep. Paul Ryan’s fiscal plan as “right-wing social engineering" and reports of a $500,000 line of credit to Tiffany’s, the luxury jewelry company.

Gary Johnson, announced on April 21

Jim Cole
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AP

Former New Mexico Gov. Gary Johnson

The former New Mexico governor took a big leap in late April, not by announcing an exploratory committee, but by actually announcing his official candidacy. “I’m running for president of the United States,” he told a couple of supporters and cameramen gathered for his announcement outside the New Hampshire State Capitol.

He's a steadfast libertarian who supports the legalization of marijuana. He vetoed more than 700 pieces of legislation during his two terms as governor.